Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0025202 (melanoma)
 69,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tyrosinase is a rate-limiting enzyme in melanin biosynthesis and is specifically expressed in differentiated melanocytes. We have identified the enhancer element in the 5'-flanking region of the human tyrosinase gene that is responsible for its pigment cell-specific transcription and have termed it tyrosinase distal element (TDE) (positions -1861 to -1842). Transient expression assays showed that TDE confers efficient expression of a firefly luciferase reporter gene linked to the tyrosinase gene promoter in MeWo pigmented melanoma cells but not in HeLa cells, which do not express tyrosinase. TDE was specifically bound by nuclear proteins of MeWo and HeLa cells, the binding properties of which were indistinguishable in gel mobility shift assays. TDE contains the CATGTG motif in its center, and mutation analysis indicates that the CA dinucleotides of this motif are crucial for protein binding and pigment cell-specific enhancer function. The CATGTG motif is consistent with the consensus sequence recognized by a large family of transcription factors with a basic helix-loop-helix structure, which prompted us to examine the possible involvement of a ubiquitous transcription factor, USF, and a novel factor, microphthalmia-associated transcription factor (MITF), recently cloned as the human homolog of the mouse microphthalmia (mi) gene product. The mi phenotype is associated with a mutant mi locus and characterized by small eyes and loss of melanin pigments. Both USF and MITF are predicted to contain a basic helix-loop-helix structure and a leucine zipper structure. We provide evidence that USF binds to TDE, whereas we were unable to detect the DNA-binding activity of MITF. Transient coexpression assays showed that MITF specifically transactivates the promoter activity of the tyrosinase gene through the CATGTG motif of TDE but not the promoter of the ubiquitously expressed heme oxygenase gene, while USF is able to activate both promoters. These results indicate that MITF is a cell-type-specific factor that is capable of activating transcription of the tyrosinase gene.
 ...
PMID:Microphthalmia-associated transcription factor as a regulator for melanocyte-specific transcription of the human tyrosinase gene. 786 73

Microphthalmia-associated transcription factor (MITF), the human homolog of the mouse microphthalmia gene product, regulates melanocyte-specific transcription of the tyrosinase gene that codes for an essential enzyme in melanin biosynthesis. In this study, we have cloned and characterized the human genomic DNA segment containing a melanocyte-type exon and its 5'-flanking region of the MITF gene. A major transcriptional initiation site was assigned by primer extension and S1 nuclease mapping analyses using melanoma RNA. Subsequently, the fusion genes, containing the identified 5'-flanking region upstream from the firefly luciferase gene, were constructed and were introduced into pigmented melanoma cells or HeLa cells which do not express MITF mRNA. Transient expression assays show that the 5'-flanking region of 2.3 kb is able to confer preferential expression of a luciferase gene in pigment cells. These results establish that the MITF gene contains a melanocyte-specific promoter.
 ...
PMID:Identification of a melanocyte-type promoter of the microphthalmia-associated transcription factor gene. 864 45

The rate-limiting step in melanogenesis is catalyzed by tyrosinase, a multifunctional enzyme encoded by the albino locus. We have previously reported that depletion of protein kinase C by long-term treatment of B16 mouse melanoma cells with phorbol dibutyrate (PDBu) prevented cell density-dependent melanogenesis. This was accompanied by a lack of induction of tyrosinase protein and mRNA. We report here the effect of PDBu on the functional activity of the mouse tyrosinase promoter by reporter gene assay and its effect on the binding of nuclear proteins from B16 cells to the "M-box" region of the mouse tyrosinase promoter. Short-term PDBu treatment of B16 cells transfected with a mouse tyrosinase promoter-luciferase construct resulted in increased reporter gene activity, while long-term PDBu treatment inhibited reporter gene activity. Using an oligonucleotide containing the M-box and its flanking residues in electrophoretic mobility shift assays, we found a density-dependent change in the pattern of DNA-protein complexes. One complex was found to be negatively regulated by long-term PDBu treatment. Competition experiments with various mutated oligonucleotides demonstrated that both the M-box and flanking residues are important for nuclear protein binding. The complex whose formation was inhibited by long-term PDBu treatment was shown to contain the basic helix-loop-helix leucine zipper protein microphthalmia-associated transcription factor (MITF). These results suggest that chronic PDBu treatment might inhibit tyrosinase expression (and subsequent melanogenesis) by affecting the amount or function of MITF.
 ...
PMID:Characterization of density-dependent regulation of the tyrosinase gene promoter: role of protein kinase C. 941 70

Mutations at the mouse locus encoding microphthalmia-associated transcription factor (Mitf) affect the development of many cell types, including retinal pigment epithelium (RPE), melanocytes, mast cells, and osteoclasts. Here we have identified a novel Mitf isoform, Mitf-a, and its human homologue MITF-A by cDNA cloning. MITF-A consists of 520 amino acid residues and differs in the amino-terminus from authentic melanocyte-type MITF (MITF-M). MITF-A mRNA is widely expressed and represents a predominant MITF isoform in cultured RPE cells, whereas MITF-M mRNA is exclusively expressed in melanocytes and melanoma cells. In situ hybridization analysis suggested that Mitf-a mRNA is enriched in the prospective RPE of mouse embryo. Moreover, transient cotransfection assays suggested that MITF-A activated transcription of the tyrosinase and tyrosinase-related protein 1 genes. MITF-A/Mitf-a therefore may play an important role in melanogenesis in RPE.
 ...
PMID:Identification of a novel isoform of microphthalmia-associated transcription factor that is enriched in retinal pigment epithelium. 964 58

Among more than 80 different loci related to mouse coat color, microphthalmia-associated transcription factor (Mitf) encoded at the mouse microphthalmia locus is one of the most exciting molecules that regulates the development and survival of many cell types, including melanocyte, retinal pigment epithelium (RPE), and mast cells. Mitf and its human homolog MITF consist of at least three isoforms, referred to as Mitf-A/MITF-A, the heart-type Mitf-H/MITF-H, and the melanocyte lineage-specific Mitf-M/MITF-M, respectively. These isoforms differ in the amino-terminal domains but share a transactivation domain and a basic helix-loop-helix and leucine-zipper structure that is required for DNA binding and dimerization. MITF-M is exclusively expressed in melanocytes and melanoma cells, but not in other cell types, including RPE cells. In contrast, MITF-A mRNA is widely expressed in many cell types. These three isoform mRNAs are possibly generated by differential usage of the gene promoters and by alternative splicing. We predict that the entire MITF gene spans about 200 kb of DNA. Like MITF-M, MITF-A is able to activate the two melanogenesis gene promoters, tyrosinase and tyrosinase-related protein 1. These results suggest that melanogenesis may be regulated by different MITF isoforms in melanocyte and RPE. Possible implications of the multiplicity in Mitf/MITF isoforms are discussed.
 ...
PMID:A big gene linked to small eyes encodes multiple Mitf isoforms: many promoters make light work. 987 May 44

Microphthalmia-associated transcription factor (MITF) is the human homolog of a basic helix-loop-helix-leucine zipper protein (Mitf), encoded by the mouse microphthalmia locus. Mutations in the MITF gene have been identified in some patients with Waardenburg syndrome type 2 (WS2), which is a dominantly inherited disorder, characterized by varying combinations of sensorineural hearing loss and pigmentary disturbances. Furthermore, mice with mutations at the Mitf locus are associated with various phenotypes, such as white coat color, small eyes, a deficiency in mast cells, and osteopetrosis. Thus, MITF/Mitf may play an important role in differentiation of melanocytes and some other cell types. Recently we have identified two MITF isoforms with extended amino-termini, MITF-A and MITF-H. Both isoforms possess unique amino-termini that are different from the amino-terminus of the originally identified melanocyte-specific MITF (MITF-M). MITF-M mRNA is exclusively expressed in melanocytes and pigmented melanoma cells, whereas MITF-A and MITF-H mRNA are widely expressed in many cell types, including retinal pigment epithelium. Transient transfection assays suggested that these isoforms possess differential transactivation capacity. It is therefore conceivable that the previously identified mutations may alter the functions of not only MITF-M but also MITF-A and MITF-H. Possible implications of the MITF isoform multiplicity in the pathogenesis of auditory-pigmentary disorders are discussed.
 ...
PMID:Implications of isoform multiplicity of microphthalmia-associated transcription factor in the pathogenesis of auditory-pigmentary syndromes. 1053 82

The basic helix-loop-helix/leucine zipper (bHLH/ZIP) microphthalmia-associated transcription factor (MITF) regulates transcription of genes encoding enzymes essential for melanin biosynthesis in melanocytes and retinal pigmented epithelial cells. To determine how MITF activity is regulated, we used the yeast two-hybrid system to identify proteins expressed by human melanoma cells that interact with MITF. The majority of clones that showed positive interaction with a 158-amino-acid region of MITF containing the bHLH/ZIP domain (aa 168-325) encoded the ubiquitin conjugating enzyme hUBC9. The association of MITF with hUBC9 was further confirmed by an in vitro GST pull-down assay. Although hUBC9 is known to interact preferentially with SENTRIN/SUMO1, in vitro transcription/translation analysis demonstrated greater association of MITF with ubiquitin than with SENTRIN. Importantly, cotransfection of MITF and hUBC9 expression vectors resulted in MITF protein degradation. MITF protein was stabilized by the proteasome inhibitor MG132, indicating the role of the ubiquitin-proteasome system in MITF degradation. Serine 73, which is located in a region rich in proline, glutamic acid, serine, and threonine (PEST), regulates MITF protein stability, since a serine to alanine mutation prevented hUBC9-mediated MITF (S73A) degradation. Furthermore, we identified lysine 201 as a potential ubiquitination site. A lysine to arginine mutation abolished MITF (K201R) degradation by hUBC9 in vivo. Our experiments indicate that by targeting MITF for proteasome degradation, hUBC9 is a critical regulator of melanocyte differentiation.
 ...
PMID:Regulation of microphthalmia-associated transcription factor MITF protein levels by association with the ubiquitin-conjugating enzyme hUBC9. 1069 30

Microphthalmia-associated transcription factor (Mitf) plays a critical role in the development of neural crest-derived melanocytes. Here, we show that exogenously added Wnt-3a protein, an intercellular signaling molecule, up-regulates the expression of endogenous melanocyte-specific Mitf (Mitf-M) mRNA in cultured melanocytes. The melanocyte-specific promoter of the human MITF gene (MITF-M promoter) contains a functional LEF-1-binding site, which is bound in vitro by LEF-1 and confers the preferential expression on a reporter gene in melanocytes and melanoma cells, as judged by the transient transfection assays. Moreover, the LEF-1-binding site is required for the transactivation of a reporter gene by LEF-1, beta-catenin, or their combination. Exogenously added Wnt-3a protein also transactivates the MITF-M promoter via the LEF-1-binding site; this activation was abolished when a dominant-negative form of LEF-1 was coexpressed. These results suggest that Wnt-3a signaling recruits beta-catenin and LEF-1 to the LEF-1-binding site of the MITF-M promoter. Therefore, the present study identifies Mitf-M/MITF-M as a direct target of Wnt signaling.
 ...
PMID:Induction of melanocyte-specific microphthalmia-associated transcription factor by Wnt-3a. 1074 53

Microphthalmia-associated transcription factor (MITF) affects the development of many types of cells, including melanocytes and retinal pigment epithelium (RPE). MITF consists of at least three isoforms, MITF-A, MITF-H and MITF-M, differing at their amino-termini and expression patterns. Here, we characterize the structural organization of the human MITF gene. The gene contains at least four isoform-specific first exons, exons 1A, 1H, 1B and 1M in the 5' to 3' direction, each of which encodes the unique amino-terminus of a given isoform, including newly identified MITF-B. The 5'-flanking regions of these isoform-specific exons are termed promoters A, H, B and M, respectively, which showed different promoter activities, as judged by transient transfection assay. Promoter A directs the expression of a reporter gene in RPE, cervical cancer and melanoma cells, whereas promoter M is functional only in melanoma cells. Promoter H showed the significant activity in RPE and cervical cancer cells but not in melanoma cells. In contrast, the 1.7 kb 5'-flanking region of exon 1B showed no noticeable promoter activity in these cell lines. Therefore, alternative promoters provide the MITF gene with the diversity in transcriptional regulation and the capability of generating structurally different protein isoforms.
 ...
PMID:Structural organization of the human microphthalmia-associated transcription factor gene containing four alternative promoters. 1076 May 82

Commitment to the melanocyte lineage is characterized by the onset of microphthalmia-associated transcription factor (Mitf) expression. Mitf plays a fundamental role in melanocyte development, with mice lacking Mitf being entirely devoid of pigment cells. In the absence of functional Mitf protein, melanoblasts expressing Mitf mRNA disappear around 2 days after their first appearance either by apoptosis or by losing their identity and adopting an alternative cell fate. The role of Mitf must therefore be to regulate genes required for melanoblast survival, proliferation, or the maintenance of melanoblast identity. Yet to date, Mitf has been shown to regulate genes such as Tyrosinase, Tyrp-1, and Dct, which are required for pigmentation, a differentiation-specific process. Because expression of these genes cannot account for the complete absence of pigment cells in Mitf-negative mice, Mitf must regulate the expression of other as yet uncharacterized genes. Here we provide several lines of evidence to suggest that Mitf may regulate the expression of the Tbx2 transcription factor, a member of the T-box family of proteins implicated in the maintenance of cell identity. First, isolation and sequencing of the entire murine Tbx2 gene revealed that the Tbx2 promoter contains a full consensus Mitf recognition element; second, Mitf could bind the promoter in vitro and activate Tbx2 expression in vivo in an E box-dependent fashion; and third, Tbx2 is expressed in melanoma cell lines expressing Mitf, but not in a line in which Mitf expression was not detectable. Taken together, with the fact that Tbx2 is expressed in Mitf-positive melanoblasts and melanocytes, but not in Mitf-negative melanoblast precursor cells, the evidence suggests that the Tbx2 gene may represent one of the first known targets for Mitf that is not a gene involved directly in the manufacture of pigment.
 ...
PMID:The gene encoding the T-box factor Tbx2 is a target for the microphthalmia-associated transcription factor in melanocytes. 1077 Sep 22


1 2 3 4 5 6 7 8 9 10 Next >>